Local campaigner Brenda Dry took the case to court in a bid to halt the planned development, which was approved in October last year and backed by the High Court in June.
In a hearing last month, her lawyers argued that the planning authority, West Oxfordshire District Council, had not given enough thought to the potential for flood problems on land east of Eynsham.
But Lord Justice Carnwath, Lord Justice Maurice Kay and Lord Justice Patten have now rejected her challenge. Lord Justice Carnwath said it is a matter of planning judgment for the council to decide what weight - if any - to give to flooding.
"Whether or not the council was justified in taking such a narrow view of the flooding issue, the issue has in fact been fully considered in accordance with the requirements of the Environment Agency on the basis of detailed reports by the developers," he found.
"There is no reason to think that, on that aspect, a formal requirement for an environmental assessment would have made any difference of any practical value to the applicant," he added.